Vista update problems

My mom has a Dell Inspiron 1501 loaded with Vista. The laptop is grossly underpowered, but I have worked to keep it running. Recently it suffered the dreaded Welcome screen hang and using a restore point in safe mode, I tracked it down to a MS update. After hiding the update, the computer booted several times successfully. Then several days later it did it again. I booted it up in safe mode again and found not only were the all the restore points gone, but the control panel blinked away about half of the Apps, including the Security Center, so there is no way to return to a previous condition or remove another possible rogue update. The computer is only used for internet and email, so a re-install is no problem. I have an extra XP license, so I'm thinking chucking Vista for a faster OS. Any idea what happened or advice on a solution? Thx

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